1. Field
The present disclosure is directed to wireless communication transmitters. More particularly, the present disclosure is directed to adjusting transmitter power amplifiers based on resource block allocation to optimize a tradeoff between transmitter power amplifier linearity and transmitter power amplifier efficiency.
2. Introduction
Presently, wireless communication devices, such as handsets, mobile phones, personal digital assistants, tablets, laptop computers, and other wireless communication devices are used to wirelessly transmit communication signals over a network and between wireless communication devices and servers. New and future applications and services, such as streaming video and audio and large file transfers, as well as better voice quality, require higher and higher data rates for wireless transfer of the corresponding data. To transmit the data the wireless communication devices use power amplifiers to amplify the data communication signals.
Unfortunately, as data rates increase in wireless communication networks and handsets, power amplifier current drain tends to worsen. The power amplifier current drain worsens for two reasons. First, digitally modulated signals supporting high data rates have high peak to average ratios (PAR), meaning more linear headroom is needed in the power amplifier. This leads to LTE power amplifier efficiencies in the 40% range. This means more than half of the energy drawn out of the battery by the power amplifier is wasted as dissipated heat. In fact, the power amplifier is the largest current drain and heat contributor when a wireless device is transmitting at maximum power.
The second reason the power amplifier current drain worsens is because high data rate signals increase the probability of the wireless communication device transmitting at high output power. A first order analysis shows that in order to maintain a constant energy per bit, high bit rate signals need more transmit power. A deeper look reveals that higher order modulation types, such as 16-Quadrature Amplitude Modulation (16-QAM) vs. Quadrature Phase Shift Keying (QPSK) require a higher Signal to Noise Ratio (SNR) at the base station receiver. This means the wireless communication device requires more transmit power. Wider Resource Block (RB) allocations also require an increase in total transmit power to maintain a constant power per RB. The net effect of low power amplifier efficiency and high transmit power probability is a reduction in handset battery life, and an increase in heat dissipation.
Thus, there is a need for a method and apparatus for resource block based transmitter optimization in wireless communication devices.